Generally, as systems for drive-controlling three-phase brushless motors (hereinafter, simply referred to as “motors”) to be used as starter motors and alternate current power generators of internal combustions (engines), sensor drive control circuits have been known. In a sensor drive control circuit, multiple hole devices for detecting the position of a rotor (on the permanent magnet side) in a three-phase brushless motor are mounted around the rotor. However, the sensor drive control circuit requires that multiple hole devices be provided in the motor and requires that a magnet or the like for detecting the position of the rotor be mounted separately from the rotor as needed, thereby interfering with miniaturization and cost reduction of the motor. Additionally, the precision of detecting the position of the rotor occasionally varies depending on the mounted state of the hole device. For this reason, implementation of a sensorless drive control circuit that detects the position of a rotor without using a sensor such as a hole device has been strongly demanded.
For example, there is a battery charging device that: generates a rectangular wave synchronized with zero-cross points of the AC output voltage of one of the three phases of a three-phase brushless motor (brushless motor that functions as an AC power generator), which is detected by a sub-coil Su in the three-phase brushless motor; generates, based on that rectangular wave, rectangular waves synchronized with the two other phases; and then, based on those rectangular waves (rotor position detection waveforms), rectifies and phase-controls the AC output voltage of the three-phase brushless motor (three-phase AC power generator) (see Patent Document 1).
Additionally, similarly, there is a brushless motor control apparatus that: includes a sub-coil Su that detects the AC output voltage of one of the three phases of the three-phase brushless motor; generates a rectangular wave synchronized with zero-cross points of the AC output voltage of the one phase detected by that sub-coil Su; generates, based on that rectangular wave, rectangular waves synchronized with the two other phases; estimates the position of a rotor based on those rectangular waves (rotor position detection waveforms); and drive-controls the brushless motor (see Patent Document 2).
Further, there is a related control device for a hybrid vehicle (see Patent Document 3). An object of the control device for the hybrid vehicle disclosed in Patent Document 3 is to ensure a desired degree of silence while increasing the precision of detecting the position of a magnetic pole.